1. Technical Field
The present invention relates to a technique for preventing burn-in and a flicker from occurring.
2. Related Art
In a liquid crystal display device, in general, a liquid crystal device is AC-driven. However, when the liquid crystal device is simply AC-driven, a direct-current component is sometimes applied to liquid crystal. Specifically, in the liquid crystal display device, a pixel electrode substrate and an opposed electrode substrate provided across a liquid crystal layer have different physical structures. On an interface of an electrode and an orientated film and an interface of the oriented film and the liquid crystal layer, resistance is different when a positive voltage higher in order with respect to the opposed electrode is applied to the pixel electrode substrate and when a negative voltage lower in order with respect to the opposed electrode is applied. Consequently, in the liquid crystal display device, even if an effective voltage applied to the liquid crystal layer is equal when the positive voltage is applied and when the negative voltage is applied, a current amount is different and asymmetry occurs in the movement of charges. Because of the asymmetry of the current amount, a bias occurs in charges in the liquid crystal. An internal electric field is generated by the bias of the charges. Because of the influence of the internal electric field, a voltage actually applied to the liquid crystal layer becomes asymmetry according to the polarity of a driving voltage. A direct-current voltage component is applied to the liquid crystal layer.
When the direct-current voltage component is applied to the liquid crystal layer, a flicker occurs. Therefore, there is a technique for adjusting the voltage of the opposed electrode in order to prevent the flicker. For example, an adjusting circuit disclosed in JP-A-8-286169 measures, with an optical sensor, luminance obtained when the positive voltage is applied to the liquid crystal device and luminance obtained when the negative voltage is applied to the liquid crystal device and adjusts the voltage of the opposed electrode on the basis of a difference between the luminance obtained when the positive voltage is applied and the luminance obtained when the negative voltage is applied.
Even if the voltage of the opposed electrode is adjusted by the adjusting circuit disclosed in JP-A-8-286169 to minimize the flicker, the direct-current voltage component is applied to the liquid crystal device because of aged deterioration and burn-in occurs. In this case, an operator operates the adjusting circuit again to cause the adjusting circuit to adjust the voltage of the opposed electrode. This is time-consuming.